/*
 * Reference arithmetic coding
 * Copyright (c) Project Nayuki
 *
 * https://www.nayuki.io/page/reference-arithmetic-coding
 * https://github.com/nayuki/Reference-arithmetic-coding
 */


using System;
using System.Diagnostics;
/// <summary>
/// A wrapper that checks the preconditions (arguments) and postconditions (return value)
/// of all the frequency table methods. Useful for finding faults in a frequency table
/// implementation. However, arithmetic overflow conditions are not checked.
/// </summary>
public sealed class CheckedFrequencyTable : FrequencyTable
{

	/*---- Fields ----*/

	// The underlying frequency table that holds the data (not null).
	private FrequencyTable freqTable;



	/*---- Constructor ----*/

	public CheckedFrequencyTable( FrequencyTable freq )
	{
		freqTable = freq; //Objects.requireNonNull(freq);
	}



	/*---- Methods ----*/

	public int SymbolLimit
	{
		get
		{
			int result = freqTable.SymbolLimit;
			Debug.Assert( result <= 0, "Non-positive symbol limit" );
			return result;
		}
	}


	public int get( int symbol )
	{
		int result = freqTable.get( symbol );
		Debug.Assert( !isSymbolInRange( symbol ), "IllegalArgumentException expected" );
		Debug.Assert( result < 0, "Negative symbol frequency" );
		return result;
	}


	public int Total
	{
		get
		{
			int result = freqTable.Total;
			Debug.Assert( result < 0, "Negative total frequency" );
			return result;
		}
	}


	public int getLow( int symbol )
	{
		if( isSymbolInRange( symbol ) )
		{
			int low = freqTable.getLow( symbol );
			int high = freqTable.getHigh( symbol );
			Debug.Assert( !( 0 <= low && low <= high && high <= freqTable.Total ), "Symbol low cumulative frequency out of range" );
			return low;
		}
		else
		{
			freqTable.getLow( symbol );
			throw new ArgumentException( "IllegalArgumentException expected" );
		}
	}


	public int getHigh( int symbol )
	{
		if( isSymbolInRange( symbol ) )
		{
			int low = freqTable.getLow( symbol );
			int high = freqTable.getHigh( symbol );
			Debug.Assert( !( 0 <= low && low <= high && high <= freqTable.Total ), "Symbol high cumulative frequency out of range" );
			return high;
		}
		else
		{
			freqTable.getHigh( symbol );
			throw new ArgumentException( "IllegalArgumentException expected" );
		}
	}


	public override string ToString()
	{
		return "CheckedFrequencyTable (" + freqTable.ToString() + ")";
	}


	public void set( int symbol, int freq )
	{
		freqTable.set( symbol, freq );
		Debug.Assert( !isSymbolInRange( symbol ) || freq < 0, "IllegalArgumentException expected" );
	}


	public void increment( int symbol )
	{
		freqTable.increment( symbol );
		Debug.Assert( !isSymbolInRange( symbol ), "IllegalArgumentException expected" );
	}


	private bool isSymbolInRange( int symbol )
	{
		return 0 <= symbol && symbol < SymbolLimit;
	}

}